1. Field of the Invention
The present invention relates to netrin-1, compositions thereof, and methods of treatment employing netrin-1.
2. Description of the Related Art
Netrin-1 is a secreted molecule that is largely known to play a defined role in guiding vertebrate commissural axons in neuronal development. See Kennedy et al. (1994) Cell 78:425-35; Serafini et al. (1994) Cell 78:409-24; and Serafini et al. (1996) Cell 87:1001-14. Recent studies have further demonstrated a critical role of netrin-1 in endothelial cell proliferation, migration and angiogenic signaling, in addition to morphogenesis of epithelial cells. See Park et al. (2004) PNAS USA 101:16210-5; Lu et al. (2004) Nature 432:179-86; Carmeliet et al. (2005) Nature 436:193-200; Nguyen et al. (2006) PNAS USA 103:6530-5; Wilson et al. (2006) Science 313:640-4; Navankasattusas et al. (2008) Development 135:659-67; Liu et al. (2004) Curr Biol 14:897-905; and Nikolopoulos et al. (2005) Cell Cycle 4:e131-5. At least eight netrin receptors have been characterized in neurons, vascular system and other cell types in mammals. These include deleted in colorectal cancer (DCC), UNC5A, B, C, D, neogenin, a6β4 and α3β1 integrins. See Tessier-Lavigne et al. (1996) Science 274:1123-33; Huber et al. (2003) Annu Rev Neurosci 26:509-63; Cirulli et al. (2007) Nat Rev Mol Cell Biol 8:296-306; and Yebra et al. (2003) Dev Cell 5:695-707. Netrin-1 binding to DCC mediates attractive outgrowth of axons, as well as positive angiogenic signalings in endothelial and vascular smooth muscle cells. In contrast, the UNC5B receptor appears repulsive, mediating cellular effects such as filopodial retraction, particularly in developing capillaries. See Lu et al. (2004) Nature 432:179-86; and Larrivee et al. (2007) Genes Dev 21:2433-47.
In a recent study it was found that netrin-1 induces production of nitric oxide (NO) to promote aortic endothelial cell migration and proliferation. See Nguyen et al. (2006) PNAS USA 103:6530-5. It was also found that netrin-1 induced NO production is DCC-dependent, involving a feed-forward activation of ERK1/2-eNOS. Binding of netrin-1 to DCC leads to an initial activation of ERK1/2, consequent phosphorylation and activation of eNOS as well as production of NO, which in turn further activates ERK1/2 and more NO production to prompt endothelial cell growth and migration. It has been established that a deficiency in endothelial nitric oxide synthase (eNOS) exacerbates myocardial I/R injury, whereby eNOS overexpression, NO donor, or dietary supplementation of nitrite significantly improved cardiac function in models of hypoxia and myocardial I/R injury, however with unclear molecular mechanisms. See Elrod et al. (2006) Arterioscler Thromb Vasc Biol 26:1517-23; Jones et al. (2004) Am J Physiol Heart Circ Physiol 286:H276-82; Pabla et al. (1996) Circ Res 78:65-72; Siegfried et al. (1992) Am J Physiol 263:H771-7; and Hataishi et al. (2006) Am J Physiol Heart Circ Physiol 291:H379-84. In addition, netrin-1 has been shown to protect against renal I/R injury in vivo, with unknown molecular/signaling mechanisms. See Wang et al. (2008) Am J Physiol Renal Physiol 294(4):F739-47. However, the overall expression profile of netrin-1 receptors in the heart has remained completely unknown; and that the effects and molecular mechanisms of netrin-1 on cardioprotection during I/R, and practical treatment methods for such, has never been explored previously.